Circuit Description

The ECM compares waveform of oxygen sensor located in front of catalytic converter with the waveform of oxygen sensor located behind catalytic converter to determine if catalytic converter performance has deteriorated. If catalytic converter is functioning properly, waveform of oxygen sensor after catalytic converter should switch back and forth between rich and lean much more slowly than waveform of oxygen sensor in front of catalytic converter.

DTC is set if after driving vehicle for 5 minutes at 20-50 MPH and engine is at normal operating temperature, oxygen sensor waveforms are the same. Possible causes are:

• Exhaust gas leak.
• Catalytic converter.
• Oxygen sensor circuit open or shorted.
• Oxygen sensor.